1. Field of the Invention
This invention relates to low-velocity electron excited phosphor for a fluorescent display device used as a display for a domestic electric appliance, an automobile, an electronic game machine, a terminal equipment of a computer or the like and a process for preparing the same, and more particularly to low-velocity electron excited phosphor comprising a mixture of phosphor having high resistance and a conductive material added thereto and a process for preparing the same.
2. Description of the Prior Art
In general, a fluorescent display device, as shown in FIG. 7, is generally constructed in a manner such that a flat box-type casing 20 of which a part is used as an anode substrate 14 is provided, and wiring conductors 15 and insulating layers 16 formed with through-holes 17a are laminated in turn on the anode substrate 14. On the insulating layers 16 are arranged anode conductors 17 in a pattern shape which are electrically connected to the wiring conductors 15 via the through-holes 17a. The anode conductors 17 each have a low-velocity electron excited phosphor layer (hereinafter referred to as "phosphor layer") 18 deposited thereon, resulting in each combination of the anode conductor 17 and phosphor layer 18 constituting each anode 19. Above the anodes 19 are stretchedly arranged control electrodes 11 and filamentary cathodes 12 in order so as to be opposite to the anodes. Thus, the conventional fluorescent display device constructed as described above causes each of the insulating layers 16 to be exposed at the portion thereof positioned at the periphery of the phosphor layer 18.
In the conventional fluorescent display device constructed as described above, electrons emitted from the filamentary cathodes 12 heated are selected by the control electrodes 11 and impinged on the phosphor layers 18 of the anodes 19 to which anode voltage is selectively applied to excite the phosphor layers so that the phosphor layers may emit light to carry out display of character, figure or the like.
Now, phosphor for forming the phosphor layer 18 deposited on the anode of the fluorescent display device will be described hereinafter.
Low-velocity electron excited phosphor to be used for a fluorescent display device is required to have the following characteristics:
A. It possesses suitable electric conductivity;
B. It is essentially low in luminous threshold;
C. It exhibits satisfied luminous efficiency under low-velocity electron excitation and does not cause the saturation of luminance;
D. It is stable against a heat treatment in the manufacturing process of a fluorescent display device and an environment in the process; and
E. It has a prolonged life under low-velocity electron excitation.
As is apparent from the above, important one of requirements for low-velocity electron excited phosphor is that it has suitable electric conductivity. In generl, phosphor is divided into three types depending upon a way of providing it with electrical conductivity, as follows:
i. Low-resistance matrix-type phosphor
Phosphor of the first type uses a conductive material as its parent material, as in a ZnO:Zn or SnO.sub.2 :Eu phosphor.
ii. Mixture-type phosphor
Phosphor of the second type consists of a mixture of phosphor used for a cathode ray tube of a color television and the like, such as, for example;
Y.sub.2 O.sub.2 S:Eu; Y.sub.2 O.sub.3 :Eu; YVO.sub.4 :Eu; (Zn.sub.1-x Cd.sub.x)S:Ag 0.65 &lt;x.ltoreq.0.9; Zn.sub.3 (PO.sub.4).sub.2 :Mn; Cd.sub.2 B.sub.2 O.sub.5 :Mn; Zn(S.sub.1-x Se.sub.x):Cu 0.05.ltoreq.x.ltoreq.0.6; Zn(S.sub.1-x Se.sub.x):Cu,Al 0.05.ltoreq.x&lt;0.6; (Zn.sub.1-x Cd.sub.x)S:Ag,Al 0.5&lt;x.ltoreq.0.7; (Zn.sub.1-x Cd.sub.x)S:Au,Al 0.ltoreq.x.ltoreq.0.2; (Zn.sub.1-x Cd.sub.x):Cu 0.1&lt;x.ltoreq.0.2; (Zn.sub.1-x Cd.sub.x)S:Cu,Al 0.1&lt;x.ltoreq.0.2; CaSiO.sub.3 :Pb,Mn; (Zn.sub.1-x Cd.sub.x)S:Cu,Al 0.ltoreq.x.ltoreq.0.1; SrGa.sub.2 S.sub.4 :Eu.sup.2+ ; Y.sub.3 (Al.sub.1-x Ga.sub.x).sub.5 O.sub.12 :Ce 0.ltoreq.x.ltoreq.0.5; Zn.sub.2 SiO.sub.4 :Mn; Y.sub.2 O.sub.2 S:Tb; La.sub.2 O.sub.2 S:Tb; (Zn.sub.1-x,Cd.sub.x)S:Ag 0.3.ltoreq.x.ltoreq.0.5; ZnS:Au,Al; ZnS:Cu,Al; ZnS:Cu,Au,Al; Zn.sub.2 SiO.sub.4 :Mn,As; (Zn.sub.1-x,Cd.sub.x)S:Cu 0.ltoreq.x.ltoreq.0.1; (Zn.sub.1-x Cd.sub.x)S:Ag,Al 0.3.ltoreq.x.ltoreq.0.5; ZnS:Ag; ZnS:Ag,Al; Zn(S,Se):Ag; Zn(S,Se):Ag,Al; Y.sub.2 SiO.sub.5 :Ce; SrGa.sub.2 S.sub.4 :Ce; Ca.sub.2 MgSiO.sub.5 :Ce; (Ca,Mg).sub.2 SiO.sub.4 :Ti; (Ba,Mg)O.sub.2.6Al.sub.2 O.sub.3 :Eu.sup.2+ ; (Sr,Ba).sub.3 (PO.sub.4).sub.2 :Eu.sup.2+ ; Ca.sub.2 B.sub.5 O.sub.9 Cl:Eu.sup.2+ PA0 Y.sub.2 O.sub.2 S:Eu; Y.sub.2 O.sub.3 :Eu; YVO.sub.4 :Eu; (Zn.sub.1-x Cd.sub.x)S:Ag 0.65&lt;x.ltoreq.0.9; Zn.sub.3 (PO.sub.4).sub.2 :Mn; Cd.sub.2 B.sub.2 O.sub.5 :Mn; Zn(S.sub.1-x Se.sub.x):Cu 0.05.ltoreq.x.ltoreq.0.6; Zn(S.sub.1-x Se.sub.x):Cu,Al 0.05.ltoreq.x&lt;0.6; (Zn.sub.1-x Cd.sub.x)S:Ag,Al 0.5&lt;x.ltoreq.0.7; (Zn.sub.1-x Cd.sub.x)S:Au,Al 0.ltoreq.x.ltoreq.0.2; (Zn.sub.1-x Cd.sub.x):Cu 0.1&lt;x.ltoreq.0.2; (Zn.sub.1-x Cd.sub.x)S:Cu,Al 0.1&lt;x.ltoreq.0.2; CaSiO.sub.3 :Pb,Mn; (Zn.sub.1-x Cd.sub.x)S:Cu,Al 0.ltoreq.x.ltoreq.0.1; SrGa.sub.2 S.sub.4 :Eu.sup.2+ ; Y.sub.3 (Al.sub.1-x Ga.sub.x).sub.5 O.sub.12 :Ce 0.ltoreq.x.ltoreq.0.5; Zn.sub.2 SiO.sub.4 :Mn; Y.sub.2 O.sub.2 S:Tb; La.sub.2 O.sub.2 S:Tb; (Zn.sub.1-x,Cd.sub.x)S:Ag 0.3.ltoreq.x.ltoreq.0.5; ZnS:Au,Al; ZnS:Cu,Al; ZnS:Cu,Au,Al; Zn.sub.2 SiO.sub.4 :Mn,As; (Zn.sub.1-x,Cd.sub.x)S:Cu 0.ltoreq.x.ltoreq.0.1; (Zn.sub.1-x Cd.sub.x)S:Ag,Al 0.3.ltoreq.x.ltoreq.0.5; ZnS:Ag; ZnS:Ag,Al; Zn(S,Se):Ag; Zn(S,Se):Ag,Al; Y.sub.2 SiO.sub.5 :Ce; SrGa.sub.2 S.sub.4 :Ce; Ca.sub.2 MgSiO.sub.5 :Ce; (Ca,Mg).sub.2 SiO.sub.4 :Ti; (Ba,Mg)O.sub.2.6Al.sub.2 O.sub.3 :Eu.sup.2+ ; (Sr,Ba).sub.3 (PO.sub.4).sub.2 :Eu.sup.2+ ; Ca.sub.2 B.sub.5 O.sub.9 Cl:Eu.sup.2+ PA0 Y.sub.2 O.sub.2 S:Eu; Y.sub.2 O.sub.3 :Eu; YVO.sub.4 :Eu; (Zn.sub.1-x Cd.sub.x)S:Ag 0.65&lt;x.ltoreq.0.9; Zn.sub.3 (PO.sub.4).sub.2 :Mn; Cd.sub.2 B.sub.2 O.sub.5 :Mn; Zn(S.sub.1-x Se.sub.x):Cu 0.05.ltoreq.x.ltoreq.0.6; Zn(S.sub.1-x Se.sub.x):Cu,Al 0.5.ltoreq.x&lt;0.6; (Zn.sub.1-x Cd.sub.x)S:Ag,Al 0.5&lt;x.ltoreq.0.7; (Zn.sub.1-x Cd.sub.x)S:Au,Al 0.ltoreq.x.ltoreq.0.2; (Zn.sub.1-x Cd.sub.x):Cu 0.1&lt;x.ltoreq.0.2; (Zn.sub.1-x Cd.sub.x)S:Cu,Al 0.1&lt;x.ltoreq.0.2; CaSiO.sub.3 :Pb,Mn; (Zn.sub.1-x Cd.sub.x)S:Cu,Al 0.ltoreq.x.ltoreq.0.1; SrGa.sub.2 S.sub.4 :Eu.sup.2+ ; Y.sub.3 (Al.sub.1-x Ga.sub.x).sub.5 O.sub.12 :Ce 0.ltoreq.x.ltoreq.0.5; Zn.sub.2 SiO.sub.4 :Mn; Y.sub.2 O.sub.2 S:Tb; La.sub.2 O.sub.2 S:Tb; (Zn.sub.1-x,Cd.sub.x)S:Ag 0.3.ltoreq.x.ltoreq.0.5; ZnS:Au,Al; ZnS:Cu,Al; ZnS:Cu,Au,Al; Zn.sub.2 SiO.sub.4 :Mn,As; (Zn.sub.1-x,Cd.sub.x)S:Cu 0.ltoreq.x.ltoreq.0.1; (Zn.sub.1-x Cd.sub.x)S:Ag,Al 0.3.ltoreq.x.ltoreq.0.5; ZnS:Ag; ZnS:Ag,Al; Zn(S,Se):Ag; Zn(S,Se):Ag,Al; Y.sub.2 SiO.sub.5 :Ce; SrGa.sub.2 S.sub.4 :Ce; Ca.sub.2 MgSiO.sub.5 :Ce; (Ca,Mg).sub.2 SiO.sub.4 :Ti; (Ba,Mg)O.sub.2.6Al.sub.2 O.sub.3 :Eu.sup.2+ ; (Sr,Ba).sub.3 (PO.sub.4).sub.2 :Eu.sup.2+ ; Ca.sub.2 B.sub.5 O.sub.9 Cl:Eu.sup.2+
or the like and a conductive material, such as, for example SnO.sub.2, In.sub.2 O.sub.3, ZnO or the like to decrease its overall resistance.
iii. Doped-type phosphor
Phosphor of the third type generally consists of an electrical insulating phosphor material and an impurity doped in the phosphor material to provide it with conductivity and includes, for example, ZnS:Ag,Zn,Al phosphor and the like.
The present invention, as described above, is directed to mixture-type phosphor and more particularly, improved mixture-type phosphor containing a conductive material in the form of fine particles having a particle size of several microns or less and adapted to be used for the formation of pattern or patterning of phosphor layers according to photolithography using photosensitive resin.
In conventional mixture-type phosphor, as a conductive material is used at least one material which is selected from the group consisting of conductive metal oxides such as indium oxide (In.sub.2 O.sub.3), zinc oxide (ZnO), tin oxide (SnO.sub.2), titanium oxide (TiO.sub.2), tungsten oxide (WO.sub.3), niobium oxide (Nb.sub.2 O.sub.3) and the like and conductive metal sulfides such as cadmium sulfide (CdS), copper sulfide (Cu.sub.2 S) and the like.
As known in the art, the division of a conductive material into fine particles permits the luminance of phosphor to be improved. For this purpose, it is advantageous to use a conductive material having a particle distribution of which median is 0.1-2.4.mu. and standard deviation is 0.7.mu. or less. The mixing ratio of the conductive material to a phosphor material in phosphor is of from 14:1 to 1:14 by weight, and the conductive material is mixed with the phosphor material while stirring by means of a mortar, ball mill or the like.
Accordingly, the conventional mixture-type phosphor is formed in such a manner as shown in FIG. 4. More particularly, a conductive material 1 is separated into two states, one being deposited on the surface of a phosphor material 2 due to physical force and the other being dispersed in a system in a manner separated from the phosphor material 2. Also, the conductive material 1 exists in the form of not only simple substances but aggregates.
The formation of pattern or patterning of phosphor layers using such conventional phosphor as described above may be carried out according to techniques widely known in the art such as printing, electro-deposition, precipitation or the like. However, such conventional techniques each have a disadvantage of failing in the fine patterning of phosphor layers with high precision. In the light of such a disadvantage, photolithography using a photosensitive resin material has been proposed and practiced for such fine patterning.
Nevertheless, the patterning of phosphor layers formed of the conventional mixture-type phosphor by photolithography often causes the conductive material to be separated from the phosphor material even when photosensitive phosphor paste is formed by mixing the phosphor material and liquid photosensitive resin together, because the conductive material exists in the states of being physically adhered to the phosphor material and separated therefrom as described above. More particularly, the patterning is carried out in such a manner as shown in FIG. 5. First, photosensitive phosphor paste 18 is applied onto the overall exposed surfaces of anode conductors 17 and insulating layers 16 arranged on an anode substrate 14 in order to form phosphor layers. Then, the phosphor layers applied are selectively exposed to ultraviolet rays so that only the phosphor layers for the pattern sections may be irradiated. Thereafter, a developer is put on the anode substrate to wash out the phosphor layers deposited on the insulating layers except the phosphor layers 18a for the pattern sections deposited on the anode conductors.
However, although such patterning permits the developer to wash out the phosphor material in the form of particles because the particles have a somewhat large size, it fails to remove the conductive material 1 by the developer since the material 1 is in the form of fine particles having a diameter of 0.1-2.4.mu. which is small sufficiently to cause it to adhere onto the insulating layers 16 as shown in FIG. 6. Also, when the developing is highly carried out, the chipping or peeling of the phosphor layer 18a for the pattern section often occurs. This causes the surface of the insulating layer 16 to be rendered conductive, resulting in a failure in insulation.